Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: F4UDOA on April 22, 2003, 08:49:09 PM
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If an aircraft has a 3G stall speed at it's gross weight of 160MPH and another has a 3G stall of 200MPH which one should be able to complete a 360 degree turn faster?
I did 3 360 degree turns then divided by 3 to get an average.
Tested the F4U-1D vrs the FW190A5 and found that they are virtually identical both with 75% fuelin both and a heavy load for weapons in the 190.
The F4U-1D = 20.8
The FW190A5= 21.06
How is this possible?
Does anyone the FW190 3G stall numbers? Annecdotally from Navy test the F4U could get on the tailof the 190 in 1.5 turns.
(http://mywebpages.comcast.net/markw4/F4UG.jpg)
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Turning rate = Acceleration / Speed.
So if the acceleration ("g") is the same, the plane with lower speed has better turn rate.
Turning radius = Speed squared / Acceleration.
Note that from the curves you posted you can calculate instantaneous turn rate (which is mainly related to wing loading). What you actually measured is sustained turn rate (where the thrust/weight -ratio is more important). Note that the curves are applicable to both F4U-1 and F4U-4 (same wing loading with same gross weight but very different power loading).
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Originally posted by F4UDOA
If an aircraft has a 3G stall speed at it's gross weight of 160MPH and another has a 3G stall of 200MPH which one should be able to complete a 360 degree turn faster?
I did 3 360 degree turns then divided by 3 to get an average.
Tested the F4U-1D vrs the FW190A5 and found that they are virtually identical both with 75% fuelin both and a heavy load for weapons in the 190.
The F4U-1D = 20.8
The FW190A5= 21.06
How is this possible?
Does anyone the FW190 3G stall numbers? Annecdotally from Navy test the F4U could get on the tailof the 190 in 1.5 turns.
Hi F4UDOA
Here is an Aces High Energy Maneuverability diagram for the F4U-1D overlaid with the Fw190-A5.
(http://www.badz.pwp.blueyonder.co.uk/Files/Images/F4U1D v Fw190A5 .jpg)
You can see that the sustained turn rates are very close to each other with a slight edge to the F4U. You will also notice that the F4U-1D can also achieve a slightly smaller turn radius than the Fw190-A5 when they are both fighting on the edge of the envelope. The diagram also shows that the F4U-1D has an advantage in instantaneous and sustained turns at all speeds below corner velocity, but the advantage is only small.
You can use the that diagram to read off the 3g stall speed for the Aces High aircraft by following that line of constant g until it cuts the stall limit curve on the envelope for the each aircraft.
To answer your original question, the aircraft with the lower stall speed should be able to complete its turn more quickly, because it will have a higher instantaneous turn rate, speed for speed, than the other one. However, you have to be careful in general terms, because if the aircraft in question has a very poor sustained turn, it may lose its energy very quickly then be out turned by an aircraft with a higher stall speed.
That's why energy managment is considered to be such a valuable skill in aircombat, and also why you need to consider instantaneous and sustained turning ability together... that's why EM diagrams are so useful :)
Hope that helps
Badboy
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F4UDOA,
Just to mention that the chart you posted gives acceleration limits, but the equivalent limit in the charts I produce is based on the 6g pilot physiological limit modelled by blackouts in Aces High. I use that 6g limit on the basis that if you lose sight, you lose the fight, so most folk don't max perform beyond 6g often, even though you sometimes can.
If you want to compare the 7g values, the 7g curve is shown on my diagram (but not noted) so you can still project a 7g corner speed if you want to.
Hope that helps.
Badboy
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Badboy,
Thanks for responding to my question.
I think the main problem I have in AH is some historic issues such as that the 1G stall for the F4U is just too high and some A/C like the FW190A5 is just to low. The 1G stall I have for the FW190A5 with a full load is 110MPH and the 1G stall for the F4U-1D at 12,000LBS is 100MPH both gear and flaps up. As you reduce weight the stall should come down but they seem to stay to high relative to weight.
I guess my main question should be if the F4U-1D has a three 3G stall at 160MPH and the 190 has an estimated historic 3G stall of 180MPH the why can't the F4U fly a 160MPH circle at max G and clearly turn inside the 190?
BTW, in the Navy comparison between these two same A/C the F4U could from a head to head merge be on the tail of the 190A5 in 1 turn.
TimRas,
Your testing really sparked my question.
It seems to me that their is to much parity in the abilitys of some A/C in AH for what reason I do not know.
Does anyone have FW190 stall test?
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Did some more off line testing.
In low 2000RPM 20"MAP reduced speed and attempted some low speed intentaneous turns. Could not get 2G's at chart indicated 126MPH. In fact I couldn't get two G's at 135MPH.
Does anyone have the same chart for other A/C?
I have the P-51D and P-38L. The P-51D list is at 8,000LBS so it harder to tell but the P-38L is definitely high as well.
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F4UDOA:
Instantaneous vs. sustained turn performance- they are not the same things. There isn't a simple linear relationship between the two.
Instantaneous turn performance is essentially the maximum turn performance you can get at a given point and velocity in time.
Once you start holding that turn for any amount of time it becomes a sustained turn. In sustained turns all sorts of other consequences of aerdoynamics emerge such as energy bleed from the drag induced by the turn etc.
The 3g limits you noted are instantaneous turn performance figures.
The 360 degree turns you did represent sustained turn performance.
Just because an a/c has a better instantaneous turn performance vs. another you shouldn't expect that it translates to a better sustained turn performance. There is no linear relationship between the two. Another one of those tricky things with aerodynamics.
Tango, XO
412th FS Braunco Mustangs
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neat-o a v-n diagram. it is for sustained performance, don't usually see that but nice info. thing that jumps out at me is that like f4u says the 1g stall speeds from badboy's chart and f4us don't match at all.
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CC Zig,
I have had an ongoing conversation with HT about stall speeds. There are two others that are off for sure. The F6F and P-38.
Does anyone have these diagrams or similar for the 190 series or any other bird?
DTango,
I am aware that they are not the same. But if you try to attain those instentanious figures in AH it is impossible at that weight.
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one thing you shoudl consider is the conversion from badboys chart of MPH (TAS) and f4u's chart of KPH (IAS) there will definitely be substantial differences, and I am slightly confused by the 10k and below thing because there is a big diff between 10k and the deck in terms of ias-tas conversion
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Zigrat,
I have the CAS conversion table for the F4U-1.
At 130Knots the error is 2Knots, at 140Knots the error is +3Knots.
So your looking at 164.5MPH instead of 161MPH. Not really very much to scream about. And when you consider the 140Knots is for 10K you have to figure that number is lower at sea level.
I just received a large document from the UK on the test of F4U's that the Brits had in WW2. In other sections of the report it mentions the 4G stall occuring at between 140knts and 150Knts at approx 11,700LBS.
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F4UDOA wrote:
I guess my main question should be if the F4U-1D has a three 3G stall at 160MPH and the 190 has an estimated historic 3G stall of 180MPH the why can't the F4U fly a 160MPH circle at max G and clearly turn inside the 190?
Your question was this no? You're assuming the F4U's instantaneous turn rate advantage means it should have the same advantage in sustained turn rate. There's no linear relationship between the two.
The lift-limit curve of Badboy's EM chart is based on knowing the stall speed of the AH a/c in level flight for the given alt and weight config. It's governed by:
V = Vstall * sqrt (g-load)
It's really hard to flight test against the lift-limit curve because below corner velocity the g-load is determined by the angle of bank of your turn that is less than the maximum bank angle you can achieve of ~80 degrees. Too much bank (probably above 50-60 degrees somewhere) and you've already exceeded the lift capability of the wing at that speed. You also need to make sure you have combat trim off as well.
Tango, XO
412th FS Braunco Mustangs
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Dtango,
Let me re-phrase my question.
The F4U-1D has a 3G stall of approx. 160MPH and the FW190A5 3G stall of Approx 190MPH.
Why is it not possible for the F4U to sustain a 3G turn of say 170MPH (10MPH above it's instentanious turn rate) and simply turn well inside the 190?
This the outcome of the Navy test.
It is also the outcome of Zigrats spreadsheet:)
It is on my webpage here
http://mywebpages.comcast.net/markw4/FW190A5.xls
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BTW Zig,
Are the EM diagrams sustained or instantanious?
One thing that your spreadsheet doesn't take into account is this.
The 1G stall speed for the F4U is based on 18"MAP and low RPM. Increasing power increases prop wash and Cl max.
At full or partial power the 3G stall speed Cl max should be much higher lowering accelerated stall speeds.
Sorry to pic Knits. Just read that myself.
Do you mind me putting your work on my Webpage? I gave you credit
;)
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Originally posted by F4UDOA
BTW, in the Navy comparison between these two same A/C the F4U could from a head to head merge be on the tail of the 190A5 in 1 turn.
As 1 turn takes some 20 secs, it means that if F4U gained 180 degs in that time, it has about 9dps advantage over A5. Even Spitfire cannot do that. I have great doubts about "anecdotal evidence" if we don't know exact circumstances of these tests.
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TimRas,
I don't by any means put 100% into these types of evaluations.
However I don't completely disregard them either. When I read that even though it sounds overstated I think based on wing loading and the known higher stall speed of the 190 that the F4U would have a turning advantage. I would like some clear data on accelerated stalls for the 190 series which I do not have. I do have many German docs on the 190 but I can't read them and I don't know if stall speeds are even listed.
So based on this
1. Navy evaluation.
2. 1G stall speeds.
3. Wing loading
4. Zigrats spreadsheet
I think I can make a case for some innaccuracy for the relative turning performances in AH.
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Originally posted by F4UDOA
CC Zig,
I have had an ongoing conversation with HT about stall speeds. There are two others that are off for sure. The F6F and P-38.
Can you add both of AH's Lavochkins to this. Pilots notes show an advised landing speed of 85 miles / hour (137km/hour).
In AH the plane has already fallen out the sky at this speed suggesting 1 g stall at least is high.
Its possible that the slats are not modelled (extending between and then below 220/200 km/hour)
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The F4U-1D has a 3G stall of approx. 160MPH and the FW190A5 3G stall of Approx 190MPH.
Why is it not possible for the F4U to sustain a 3G turn of say 170MPH (10MPH above it's instentanious turn rate) and simply turn well inside the 190?
Because you can't hold 3G's at 170 MPH for any length of time in a flat turn. The a/c bleeds E in a turn so maybe you could get 1-2 sec of 3G's as the speed decays to 160MPH. Let's say you continue the flat turn after you reach 160MPH. You would have 2 outcomes - (1)If you tried to maintain 3G's in a flat turn you would stall. (2)If you wanted to maintain a flat turn and remain in flight your turn performance would have to decrease along with the continued decay of airspeed.
Tango, XO
412th FS Braunco Mustangs
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Originally posted by F4UDOA
BTW Zig,
Are the EM diagrams sustained or instantanious?
The diagrams give both sustained and instantaneous performance. I've labled the previous diagram so that you can see which curves represent the sustained turns and which ones are instantaneous. Here it is:
(http://www.badz.pwp.blueyonder.co.uk/Files/Images/Ans1.jpg)
Badboy
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Dtango,
Ok, I understand.
But every A/C has a best sustained turn rate.
According to Zigs spreadsheet the F4U should be able to have a sustained turn of 165MPH at 18.86DPS and the FW190A5 best sustained turn should be 185MPH at 17.55 DPS.
This gives best sustained turn times.
12,000lbs F4U-1D full turn time = 19.33secs/2.7G's/radius 744.5FT
8,690Lbs FW190A5 full turn time = 20.5secs/2.8G's/radius 897FT
So there is a clear advantage.
In reality what would happen is both pilots pull beyond max sustained and both slow down.
The F4U has again a greater ability to turn at lower speeds so the harder the pull the more this should favor the F4U.
Also in reality these speeds would be lower because he cl max used in these calc's is not based on full power prop wash over the wings which greatly increase prop wash and lowers stall speeds.
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Originally posted by F4UDOA
Dtango,
Let me re-phrase my question.
The F4U-1D has a 3G stall of approx. 160MPH and the FW190A5 3G stall of Approx 190MPH.
Why is it not possible for the F4U to sustain a 3G turn of say 170MPH (10MPH above it's instentanious turn rate) and simply turn well inside the 190?
If we take the performance of the AH F4U-1D and Fw190-A5 from the EM diagram I posted earlier, and use that to predict the outcome of a one and two circle fight for the F4U-1D if it sustains a turn at 160mph and the Fw190-A5 if it sustains a turn at 190mph the situation would like this...
(http://www.badz.pwp.blueyonder.co.uk/Files/Images/Ans2.jpg)
And this... Here you can see that the F4U-1D would get a guns opportunity in less than half a turn, so you can see it isn't just the turn rate that is important, because you can see from the diagram above, that their turn rates are not very different, but you also see from the diagram below, that the difference in turn radius is really responsible for the early shot, depending on which way they turn.
(http://www.badz.pwp.blueyonder.co.uk/Files/Images/Ans3.jpg)
Of course, in this example, although the Fw190 is pulling a sustained turn at 190mph, it isn't pulling its best sustained turn, it isn't max performing. I used the speed you quoted, just as an example.
It is also worth noticing from the EM diagram that the 3g stall speed for these aircraft are instantaneous values, not sustained because they are above the sustained (Ps = 0) turning curve.
Some food for thought there :)
Hope it helps.
Badboy
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BadBoy,
I realized my error when examining the charts. Thanks for the explanation.
However I noticed two things when examining your chart compared to the G limits chart i posted.
1. Notice the 2G intantanous from AH and the real chart. The 2G stall should be about 10 to 15MPH lower.
2. You are testing with 25% fuel. This chart is for max internal load. So basically a F4U-1D in AH with 25% fuel stalls higher than a RL F4U-1D with full fuel.
Frankly I don't don't know why I am so interested considering I hardly get a chance to play more than a few hours a month. I am far more interested in the historic performance than I anything else.
Thanks for the input
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Heya,
You keep beating me to the punch getting your post in a second sooner.
I ask you, does it seem like there is an extreme parity in the turning ability of A/C in AH compared to RL?
I can't help but wonder if this is not intentional for gameplay?
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Originally posted by F4UDOA
Dtango,
Ok, I understand.
But every A/C has a best sustained turn rate.
According to Zigs spreadsheet the F4U should be able to have a sustained turn of 165MPH at 18.86DPS and the FW190A5 best sustained turn should be 185MPH at 17.55 DPS.
This gives best sustained turn times.
12,000lbs F4U-1D full turn time = 19.33secs/2.7G's/radius 744.5FT
8,690Lbs FW190A5 full turn time = 20.5secs/2.8G's/radius 897FT
So there is a clear advantage.
But that is only a small advantage, just over one degree per second difference, and not very different to the test times you posted in your original message, and not very different from the AH EM diagram above?
Badboy
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Those numbers are from the spreadsheet EM that Zig gave me.
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Originally posted by F4UDOA
Heya,
You keep beating me to the punch getting your post in a second sooner.
Yep, perhaps I type faster than you :)
Since we are both just sat at our keyboards, why not email me a voice number (Badboy@netcomuk.co.uk) so we can chat... my dime :)
I ask you, does it seem like there is an extreme parity in the turning ability of A/C in AH compared to RL?
Well, of course some aircraft appear to be similar, but others are very different so I don't think you have discovered a trend. But when you consider that it is almost impossible to find any two real world sources that agree on such data, we shouldn't be too surprised to find that the sources used in AH doesn't match what you have.
I can't help but wonder if this is not intentional for gameplay?
I doubt that very much! I have no doubt at all that every aircraft in the game represents an honest and honorable attempt to model it with the maximum fidelity possible. I've been flying simulations since 1987, and I've flown every online sim ever produced, and I can say without doubt that HTC have certainly shown more commitment to getting it right, and willingness to tweak, than any other developer I've known. In most cases I think they have done an excellent job. My guess is, that if you really want to influence their effort, this might not be the best place to do it :)
Badboy
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Originally posted by F4UDOA
Those numbers are from the spreadsheet EM that Zig gave me.
Sorry, I'm getting confused :)
Badboy
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dude my spreadsheet is just approximate mabye accurate to 10% but not exact. i wrote that thing a long time ago when i really didn't know much, i still don't know a lot but definitely more than i did then, i just had to study performance fo my qualifying exams.
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i have a little time today i am gonna look at that thing and see if i can improve it
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F4UDOA:
(1) You mentioned the best sustained turn performance #'s from Zig's spreadsheet. Badboy points out how small a differential of an advantage that is.
(2) If you look at Badboy's EM chart you'll notice best sustained turnrates and radiuses of both a/c are even closer and pretty much negligible vs. the data you quoted from Zig's worksheet.
(3) Hopefully you can see by all this that comparative turn performance can be extremely tricky to determine between a/c because if you want to compare apples to apples there all sorts of things that you need to take away as variables. Badboy's further explanation of sustained turns using the speeds of F4U at 160mph vs. Fw190A5 at 190mph is an example. At those speeds according to Badboy's charts the F4U will gain angles on the 190A5. The reason being the F4U is flying at a point of it's flight envelope that has better turn performance than the 190A5. But this isn't an apple to apple comparison. Looking again at Badboy's chart you'll notice that the 190A5 if flown in a sustained turn maintaining 160 mph would pretty much match the F4U's turn rate and radius.
(4) Looking at Badboy's EM chart again the F4U doesn't have much if any advantage for sustained turns at slower speeds.
(5) If you were at Ps=0 and lowest airspeed for Ps=0 you couldn't pull any harder without stalling or losing alt.
Tango, XO
412th FS Braunco Mustangs
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Dtango,
Err I kind of agree with you here.
1. The EM diagram that BadBoy posted is for AH. AH is off on stalls in many A/C both high and low.
2. The situation that I presented was using the best sustained turn performance for both A/C. The F4U's best turn is 20MPH slower than the FW190.
If I were to incease the speed of the F4U to equal the 190 I could pull almost 4G's and outstrip the 190 by a faster turn rate.
If I reduce the speed of the 190 to Co-E with the F4U his DPS would drop to nothing because he could no longer pull G.
The scenario I presented was best case for both. The slower the fight gets it leans more towards the F4U, but at 190MPH the F4U can still pull more G than the 190.
My issue is with the relative stalls in AH as compared to historic data. How one chooses to skin a cat is up to them.
BTW, the differences between the two are far from negligable. Zig also has instantanous data in his spreadsheet that matches pretty close to the chart posted, the AH data does not.
And most importantly, Zig's chart is 12,000lbs and Badboys is at 25% fuel which equals 11,100LBS. That is a big difference.
Zigrat,
I would really appreciate any refinement you could provide.
Is there anything you can do for acceleration? Or to account for prop wash while pulling G?
Thanks
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F4UDOA:
You've been around the block many times regarding the stall speeds :). I'm not going to get into that long discussion here. You state that they are in error in AH for different a/c. I say there isn't conclusive evidence of that. As Badboy says:
I doubt that very much! I have no doubt at all that every aircraft in the game represents an honest and honorable attempt to model it with the maximum fidelity possible. I've been flying simulations since 1987, and I've flown every online sim ever produced, and I can say without doubt that HTC have certainly shown more commitment to getting it right, and willingness to tweak, than any other developer I've known. In most cases I think they have done an excellent job. My guess is, that if you really want to influence their effort, this might not be the best place to do it.:)
Regarding AH lift limit (instantaneous turn) envelope, I've already mentioned how hard it is to flight test for that data infact I'm hardpressed to figure out a procedure to accurately flight test for it with the measures of performance feedback we've got in AH. (I had thought in the past about trying to talk HTC in opening up some of their testing facilities for access because they have alot more powerful tools and methods to allow them to do some pretty interesting testing. ;) )
Zig's spreadsheet and calcs are based on some generalized figures for thrust. Calculating thrust accurately is an extremely complex proposition especially when you're talking about a range of airspeeds you have to calculate it for. In my own EM analysis I initially tried the same method and realized that I was getting thrust calculations higher than could be obtained after doing some validation work.
Even assuming the calcs you are using in Zig's spreadsheet are accurate You could maybe pull 4G's in the F4U for maybe 1-2 seconds at 190MPH as your airspeed decays rapidly? Then it becomes really hard to figure out what the turn performance would be because we have no idea as to the rate of energy bleed of the a/c as you sustain a turn.
And again using the data that you have of best sustained turn speeds of 160mph & 190mph, ~100ft radius and 1 dps turn rate advantage could hardly be characterized as a decisive advantage in my opinion therefore negligible. But I'm persuadable on this and concede that you could say the F4U has a slight advantage with these numbers but don't think that it translates into much from an angles perspective.
Tango, XO
412th FS Braunco Mustangs
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I think something is being lost in the translation here.
If an A/C is supposed to stall at a certain speed at a certain load and it does not then it is not correct. I am not using subjective data.
I also do not wish to get into a conversation about HTC's efforts or credibility. I'm sure they do the best they can.
Based on that I don't want to get into a pissing match. But if you care to compare the data I have provided to AH data at the same load levels and prove I'm wrong the we can pick it up again.
Thankyou for your assistance.
Next subject.
Does anyone have stall data on the FW190, 109 or other.
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F4UDOA:
I don't know how we got here nor do I know where to start :). Your first question was about turn performances of F4U1-D vs the FW-190A5. I have been trying to help you understand turn performance and why you can't come to the conclusion you have with what you started with.
Then you change course and start going down the path of your flight test numbers not matching the V-n diagram you have or Badboy's chart. You've done this not realizing the aerodynamic nuances involved of which if you understood you'd realize that trying to test for accelerated stall limits is downright hard to do if not impossible to obtain with what we have available in AH.
I'm off to Disney World for a week :). Best of luck with better understanding this topic. I'm always encouraged by your passion on the subject of a/c performance. There's a lot for you to understand still.
Tango, XO
412th FS Braunco Mustangs
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DisneyLand,
Good luck! Undoubtably there are children in the equation and that means money, patience and Micky Mouse. None of those three are in my possession.
Anyway I don't wan to argue about this stuff. This is what I do to relax.
Good luck and enjoy!!
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I find it offensive and plain wrong that badboy used something that resembles a spitfire in the diagram and labeled it as Fw 190A-5.
// fats
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Originally posted by fats
I find it offensive and plain wrong that badboy used something that resembles a spitfire in the diagram and labeled it as Fw 190A-5.
Refresh your browser and take another look... But the 190 is just as dead as it was before :)
Badboy
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heh.
// fats
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ok i made some corrections and improvements. who has webspace.. i can email it to you can you can post it
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Zig!!
Mememememememememememe!!!!!
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whats your email. you can email me at gtg877d@prism.gatech.edu i will reply
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Is this flight test data or is this coming out of a flight model for a particular game?
-Blogs
Originally posted by Badboy
The diagrams give both sustained and instantaneous performance. I've labled the previous diagram so that you can see which curves represent the sustained turns and which ones are instantaneous. Here it is:
(http://www.badz.pwp.blueyonder.co.uk/Files/Images/Ans1.jpg)
Badboy
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JoeBlogs,
BadBoys EM diagram is based on AH with 25% fuel.
The acceleration diagram I posted is for real.
I cannot duplicate those stalls in AH.
The F4U chart I posted is for 12,000LBS, BadBoys EM diagram is for 25%fuel or 10,567LBS and still does not match the chart I posted.
IMHO it is not even close.
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Hi guys, I'm back from Florida :).
As a side excursion I got to visit the National Naval Aviation Museum at Pensacola N.A.S. That was a gem of a museum to visit! I had no idea it was as extensive as it was. I'll have to post some of my pics from there including one of an actual N1K2-J Shinden in a different thread.
Joeblogs - Badboy writes articles for SimHQ and has posted various EM related articles charts like the above from flight testing different aircraft from their respective simulations.
F4UDOA - what flight test procedure did you use to test the accelerated stall limits of a/c? There are two types of flight tests that are used to do this, both of which are difficult to do correctly in order to capture the data in AH. The two types of tests that I know of are either constant speed or constant g tests.
Constant speed tests are used for high performance fighters today and the technique is to fly a procedure called a "wind-up turn" where throttle is fixed, velocity is fixed, and bank angle is gently and smoothly increased until critical aoa is reached. The trick with this maneuver is that to maintain constant speed the pilot also has to continue to change nose pitch to maintain a fixed velocity while simultaneously increasing bank angle. The ideal wind-up turn is a spiral descent that gets tighter as bank angles increase and steeper in order for the aircraft to maintain constant speed.
Constant g tests are easier to do than wind-up turns and are perferred for other types of aircraft but still tricky to get right in AH. In a constant g turn, the aircraft's bank angle (which results in a specific g-load) and altitude are held constant while the speed is decreased until a stall occurs. To perform this maneuver you need to know which bank angle you want to test for and then try to maintain that bank angle which is a challenge because you will need to provide elevator input to increase aoa as speed decreases in order to maintain a constant bank angle without gaining or losing altitude.
Tango, XO
412th FS Braunco Mustangs
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dtango,
AFAIK F4UDOA's flight envelope chart from the manual is based on pull ups not turning. So if someone wants to test if the AH F4U behave like the real plane, these tests should be made with pull ups from straight flight (straight dive is ok too). There is no need to keep constant speed or constant g load, just make pull ups at various speeds at given altitude (say 100-400 mph) and record the speed and g load when the stall happens. Then just just continue testing until you are satisfied with the amount of data and then plot the curves (spreadsheets like the Excel have quick and easy curve fitting utilies).
Testing turn performance is more complicated because you have to keep altitude constant and "ball in the middle" (ie the plane should not yaw; good rudder controll). For instantaneous turn performance testing there is no need for constant g load or speed; all you need is to make level turns at various speeds at given altitude until the plane stalls and record the speed and g load at the moment of the stall (and repeat this until you are satisfied with the amount of data). For the continous turning performance testing the constant speed or g load tests are the right methods but testing procedure is a bit different. In the constant speed test you adjust g load by changing turn rate keeping speed constant until balance is found then record the g load at this given speed. In the constant g load test you keep the g load constant until balance is found and then record the speed.
Sometime ago I tried some pull up testing (10 runs at about 30k, mach 0,4-0,6) with the P-51D (I recorded data with the filming option) because there is very good real life data available for the P-51D for comaprisons (turns and pull ups, icluding lift coefficient). I won't comment results otherwise than there were no surprises for me. The problem with this kind of testing is that it takes really lot of time and effort. Easiest way to make comparisons would be to know formulas used for the AH flight model but I believe these are business secrets. After all the AH is just a game and it does not bother me much if one plane in the AH does not perform exactly like the real one. Nearly allways I visit here I saw a thread or two started by F4UDOA where he whines about something is wrong with the AH F4U if compared to the real one.
gripen
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Gripen/Dtango,
I did do test that compared sustain and instantious turns.
What I could not do, that I am whining about are instantious turns at givin speeds attempting to reach the specified G load(on the chart). I could not match these.
I also have these charts for the F8F, F7F, P-38L, and P-51B/D.
Out of all of these charts the F4U has the ability at a gross weight of 12,000LBS (a full combat load) it can pull the highest G at the Lowest speed of any at it's gross weight. The only possible exception is the P-38 which list no weight for G pulled. However the P-38 also has a 6G limit which I find to be surpisingly low.
Another interesting item is the P-51 chart which shows acceleration limits at a minimum weight of 8,000LBS. It tells you to take a max load figure of 64,000lbs(8G limit at 8,000LBS) and divide it by the higher weight to reach the new load figure. For instance at 9,000lbs the max G figure would be 7.1 G's.
It also list a 2.5G stall at 150MPH. At an adjusted gross weight of 9,000LBS the stall would be 2.22G's
For comparison use the F4U-1 chart to notice that the 2.5G stall is at approx 128Knots or 148MPH at 12,000LBS.
So even with a light P-51D a fully loaded F4U should be able to pull more G that a relatively light P-51D.
When the F4U weight is adjusted to a more modest 11,000LBS used the same G limit calculation as the P-51 the 2.5G limit is reached at 120knots or 138MPH. A pretty fair advantage over the P-51D.
I do not feel that this is represented in AH. I have done many test to show this as well as present a litirary ton of data to back it up.
In fact I have 2 other documents to show the F4U accelerated stalls to be well within these guildlines if not lower.
If this is whining then so be it.
(http://www.214th.com/ww2/usa/p51/flight_limits.gif)
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F4UDOA,
As noted above, you should do testing as pull ups to get comparable data with that manual chart. Load a F4U to about 12000 lbs, climb to say 10k and do series of accelerated stalls (pull up until stall happens) from level flight (or dive) and use filming option to record data (you can read speed and max g load afterwards from the film at the moment of the stall). Then just compare your data to 10k curve from the manual. Similar test using turning would result about 10% lower g load at the moment of the stall at same speed.
For the P-51D there is very good flight tested data available from NACA technical report server:
NACA TN 1044 (http://naca.larc.nasa.gov/reports/1946/naca-tn-1044/)
NACA TN 1719 (http://naca.larc.nasa.gov/reports/1948/naca-tn-1719/)
NACA Report 1219 (http://naca.larc.nasa.gov/reports/1955/naca-report-1219/)
Note that below mach 0,64 buffeting boundary and stall boundary are same in the case of the P-51D (it is stated several times in NACA Report 1219 and TN 1719). Above mach 0,64 buffeting is caused by compressebility, therefore charts in the NACA TN 1719 are directly comparable with the chart in the F4U manual, just calculate IAS speeds to mach values at given altitudes.
Note also that "Airplane normal force coefficient" (CN=nW/qS) in the NACA 1219 and NACA TN 1719 is same as Clmax calculation (Clmax=WAz/qS) in the NACA TN 1044, so these reports give good and accurate Clmax data too. Beauty of these reports are that there is separate data sets for the pull ups and turns. It should be also noted that reports supports each other pretty well and data sets are quite large. Using Clmax you can calculate flight envelopes for any given flying weight and there is also data for some other planes which are present in the AH (P-38, F6F and P-39) in the NACA TN 1044.
Happy testing!
gripen
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oh my god! my head's almost exploding of all these numbers, static's and long texts :eek: :(
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Hi F4UDOA,
>I also have these charts for the F8F, F7F, P-38L, and P-51B/D.
That's good data! :-) Are they available online anywhere?
Some more food for thought: The accelerated stall limits in the Operating Flight Limits charts (and I suppose in Badboy's charts, too) seem to be calculated without consideration of propeller slipstream.
Power-on stall speed usually is lower than power-off stall speed, and according to some wartime reports I've seen, fighters should normally be able to turn tighter at low speeds and low Gs than suggested by the flight limit charts.
(You could visualize it as a low-speed/low-G upward bump in the accelerated stall speed graph above, or in Badboy's diagram too.)
Another thing to consider is that these flight limits charts probably are for air speeds as indicated by the airspeed indicator, so you have to be cautious when comparing different aircraft types because they might have different errors in their respective indication.
Regards,
Henning (HoHun)
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this is giving me indegestion, doesn't how fat the pilot is matter?:eek:
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HoHun,
I can post these charts or Email them. Which ever you prefer.
Also I asked the same question about prop slip stream to Zigrat. According to him (In my understanding anyway) it doesn't make nearly as much differance in accelerated conditions as it does in 1G flight because the AOA reduces the slipstream effect.
However in 1G flight slip steam increases Clmax dramatically.
FYI. I have all of the CAS correction charts as well. The CAS speed for the 3G stall of the F4U is 164MPH from 161MPH. I can post those as well.
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BTW,
I have done the accelerated stalls as Gripen defined.
At 10K using the technique Gripen defined I attempted to match the 3G stall number indicated in the chart.
At an idle condition diving at approximately a 35 degree from 11K angle I accelerated to speeds of 160, 180 and 200MPH. It seems I could only achieve a 3G stall at a speed of approx 200MPH.
This is about 35MPH over the charted speeds. I was at 75% fuel so the weight was a couple hundred pounds light as well.
I will post the test I did. But instead of picking my test apart I would like to see someone take a shot at this other than me.
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F4UDOA,
Hm... I have a vintage AH 1.06 here and I got 3,4-3,7 g at 200 mph IAS and 10k (several runs without filming). There was no big difference between power on or of, less than 0,3 g. I used the F4U-1D, 75% fuel. Flight model might have changed since 1.06.
Anyway, power on stall is what we are interested about. Test data in the NACA TN 1719 is power on and power off in the NACA TN 1044, the NACA 1219 tests were with various power settings (more close to power on). There appears to be about 0,5 g difference if compared to manual chart of the F4U (assuming 1 knot = 1,15 mph).
gripen
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Gripen,
1.06? Is that pre digi film viewer?
I did film and viewed it on the external film viewer.
And I believe the F4U FM got heavier in 1.08.
I will post my film but I am not even close to 3G's at 165MPH.
BTW, Half a G is pretty significant and our test are about 300LBS lighter that the chart calls for.
Also if your right, and the differance is between 165MPH and 200MPH. Thats not really close.
I hardly think the Spitfire crew would be pleased if they were stalling at 30MPH higher than they should.
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fyi external viewer gives tas not ias
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F4UDOA,
I have AH 1.1X something in another box somewhere else and I'm too lazy to dl 35 megs with modem right now. Anyway, relative maneuverability appears to be in correct order; Fw 190A-5 did about 3,5 g at 200 mph IAS (with quite sharp stall) and Spit IX did well over 4. So why are you complaining? One well known writer wrote once that relative accuracy is more important than absolute in the WWII flight simulators.
gripen
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Originally posted by gripen
One well known writer wrote once that relative accuracy is more important than absolute in the WWII flight simulators.
Wise words indeed :)
Badboy
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How is a FW190A5, an Aircraft with wing loading in the neighborhood of 44LBS/Sq ft turn as well as an A/C with Wing loading at 38LBS/SQ ft?
Is this relatively close? In fact closer than the differance between Spit IX (35LBS/SQ ft fully loaded) and the F4U-1D.
Why not just make it a 2D arcade game with pretty pictures. Is this relatively close enough for you?
BTW, I don't use any annecdotal arguements to make a point. Either I have documentation that matches or I don't.
When I'm wrong I'm wrong because the engineering says so. But when I right don't tell me it's close enough.
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F4UDOA,
Well, why don't you just stop whining and enjoy the game? A simulator is it's own universe. Fly Spit or A6M if you want to turn. As another writer once wrote, you are hammering your head on wall.
gripen
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Well, why don't you just stop whining and enjoy the game?
Gripen,
This statement says exactly why I am the way I am and why you are as you are.
I do enjoy the game frequently. I have been a paying customer since the open beta and fly and enjoy AH very much. Where as you not only don't pay to play you don't even have a recent copy.
Fly Spit or A6M if you want to turn.
I haven't flown the Spit since the beta but I have flown the A6M5 quite a bit. As well as the 109G10, 190, GV's, PT's and some of my other fav's. And I have posted about issue's in many of them.
And frankly your blind criticism without testing or providing any data does not exactly give you the position of calling me a whiner.
whine ( P ) Pronunciation Key (hwn, wn)
v. whined, whin·ing, whines
v. intr.
To utter a plaintive, high-pitched, protracted sound, as in pain, fear, supplication, or complaint.
To complain or protest in a childish fashion.
To produce a sustained noise of relatively high pitch: jet engines whining.
Considering the fact that you are bringing nothing to this post other than to criticize me I think you may be the one doing the most whining.
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Wing loading isn't the only factor you have to consider with regard to turning ability. How much AoA could the wing take before stalling? Focke Wulf had excellent aerodynamicists as shown by the very effective aileron design. Lbs/sq.feet wing loading numbers don't tell you how effective that wing was in producing lift. As an example; the P-51's wing was a laminar flow airfoil design which decreased drag, but was less tolerant to high AoA compared to a conventional airfoil. Higher AoA produces more lift at the expence of bleeding more E, a typical 190 trait.
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This thread won't go away ;). For grins I did some acclerated stall limit testing on the F4U-1D.
Flight parameters: 25% fuel, alt around SL.
Constant-G tests for lift limit. As prescribed in the US Navy Flight Test Manual - holding constant bank angle in level turn until speed slowly decays to point of stall. Calculated bank angle for 3g's was ~70 degrees at 173 mph TAS. Flight test results: 3g stall at 168-174 mph. Film attached below.
F4U-1D Constant-G Test (http://www.thetongsweb.com/AH/constant-g.ahf)
Pull-up tests. Wings level pullups holding 3g's. Rapid deceleration made data collection and analysis hard to conduct. The results show this difficulty: 3g stall around ~162-190 mph. Film attached below.
F4U-1D Pull-up Test (http://www.thetongsweb.com/AH/pull-up.ahf)
Between the two types of tests the constant-g was more reliable vs. the pullup test to collect data on though tricky as it is. The constant-g tests closely match what Badboy's EM chart indicate.
Tango, XO
412th FS Braunco Mustangs
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Originally posted by GScholz
Wing loading isn't the only factor you have to consider with regard to turning ability. How much AoA could the wing take before stalling?
Another interesting question is what happens when the critical AOA is reached. If the aircraft has a severe stall with little warning, then it will be difficult for any but the most skilled to extract its maximum turn performance (especially in a low-level stallfight).
The Focke-Wulf 190 seems to have been noted as especially bad in this respect, despite its aerodynamic excellence in other areas. A computational analysis (Lednicer, 1995, in the Royal Aeronautical Society Journal) concluded that "the aerofoils and twist used on the Fw 190, combined with the wing's elastic properties are the cause of the aircraft's harsh stall characteristics."
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Dtango,
Thanks for actually listing to what I'm saying.
I looked at your film on the digital viewer and your results are very good.
I don't know if you looked through the external viewer or not but I would say you canstant 3G was about 170MPH and the pull up was about 190MPH at 3G.
Two things.
1. The Chart I am using for comparison is from the F4U-1 flight limits chart I posted not Badboy's EM chart. Badboys chart is based on AH.
2. Your test was at 25% fuel which in an F4U-1D is 11,000LBS. Or 1,000lbs less than the 12,000LBS specified in the Accelerations chart I posted. All of the Test I performed were at 75% fuel which is still underweight but not nearly so much.
Using the meathod from the P-51 chart to determine the F4U max G at a given weight multipy the charts weight by the G factor then devide by the new weight.
So 12,000lbs * 3G = 36,000lbs / 11,000LBS = 3.27.
So basically your increasing your G load by about 27% with every 1,000lbs.
I may seem like I'm being Zealous here for what may not seem like a huge difference but it is rather significant.
The problem is this. Some A/C in WW2 were excellent turning A/C ala the Spit, Zero, Hurri and some were moderate F4U, F6F, P-51, 109 (late) and some were poor P-47, FW190. The first group of excellent turning A/C IMHO are very well represented in there ability. IMHO the latter two groups are lumped into a parity of turning ability that is not realistic.
This can be seen in the 1G stalls and the accelerated stalls which are almost identical depending on loading.
What I would like to see is simple to define at least in the American A/C is to have stalls occur as the P-38, P-51, F6F, F4U as they should be. I do not have the data for the Euro types but I'm sure HTC does.
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Heyas,
So why doesn't the AH stall limits match the chart you posted for the F4U-1D? There could be hundreds of reasons. I think it's a bit premature to make the claim something is off. Let's just do some further triangulation here.
Going by the posted chart if we have 3g stall speed of 160mph at 10k ft. Running the math we get 1g stall then at 92mph TAS at 10,000 ft. Running the calculations for 92mph at 10k we get a sea level stall speed of 79 mph TAS.
What do you have a for a 1g stall speed of a F4U-1D, 12,000 lbs, at SL clean? Does it match the 79 mph?
The only data I have comes from the "Joint Fighter Conference" which I just have the figures and don't know the flight parameters (weight etc.).
Tango, XO
412th FS Braunco Mustangs
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Originally posted by Guppy
Another interesting question is what happens when the critical AOA is reached. If the aircraft has a severe stall with little warning, then it will be difficult for any but the most skilled to extract its maximum turn performance (especially in a low-level stallfight).
The Focke-Wulf 190 seems to have been noted as especially bad in this respect, despite its aerodynamic excellence in other areas. A computational analysis (Lednicer, 1995, in the Royal Aeronautical Society Journal) concluded that "the aerofoils and twist used on the Fw 190, combined with the wing's elastic properties are the cause of the aircraft's harsh stall characteristics."
Yes the 190 had very bad departure charecteristics, especially the snap-roll was deadly at low alts. I think it would be fair to say that the 190 pilots were apprehensive about pushing the envelope in turning fights ... unlike us virtual pilots ;)
I've seen LW guncam footage of an 190A8 who completely out flew a P47 in a turning fight at medium alt, turned inside him after three or four circles and scored hits. Must have been a good pilot in that A8.
I think the relative pilot quality of the two airforces were a greater factor in 44-45 than the qualities of their airplanes. Again this is not something we see in AH. That the LW was able to offer any effective resistance at all late in the war is quite amazing considering the odds stacked against them.
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I like triangulation, lets play.
The chart when CAS is corrected the 3G stall at 10K is 164MPH. The math I think you are doing is deviding by the square of the G force. So the square of 3G's is 1.73, so take 164 devided by 1.73 = 94.7MPH power on stall which corresponds very well to quoted power on stalls in the F4U CAS.
Your question is if you take that to sea level does that sound right? That being the 72MPH CAS to TAS.
The answer is no of course not. The chart I posted is IAS not TAS.
[However a subject for another thread is that clmax goes way up with increase in power and prop wash in 1G flight. So at higher power settings the 1G stall can be much lower than what is quoted.]
TAS speed is always going to be higher than IAS at higher alts. Thats why stall speeds are always quoted in IAS. The pilot can't sit there with a conversion chart while flying.
The chart does have a margin of error built into it for variations in stall as altitude increases. However at sea level it should be at the low end of that chart.
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I thought the F4U-1D was *the* worst turning US plane because of the spoiler on the wing, it gave the wing a poor life coeffiencent which kinda offset the moderate wingloading. According to AHT that is the way it was, even the P-47 turned better.
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Urchin,
Unknowingly you are the cause of this post. You outturned me in a flat turn when I thought I had you dead to rights when you were in a 190A.
Frances Dean who wrote AHT used a calculation to come up with a turning index using the CLmax of each AC clean no flaps. Oddly enough the Clmax for the F4U he used was 1.48 and is correct. However the Clmax used for the rest of his A/C are all way off to high. The P-47 Clmax he has listed as 1.93. That would give the P-47D at 14,300LBS a 1G stall of 97.5MPH clean no power. Not likely.
In fact no WW2 fighters that I am aware of had a Clmax of over 1.6 with no flaps. Mr.Dean quotes 5 a/c over 2.0 and two over 1.8. In fact the only one even close in the F4U.
While Mr.Dean was alive I visited him in his home and asked him via Email where his lift coeeficients came from. he said he calculated them from the 1944 fighter conferance(which he also published). Unfortuately the confernace results are all over the place if you have a copy you may notice that stalls in Knots and MPH are used interchangeable between A/C. Also take a look at the FG-1 stall. It is at 130Knts and is the same exact A/C as the F4U-1D. If he had used the FG-1 stall speed you would be saying the best turning WW2 fighter instead.
FYI, all except the first 800 F4U's made had the spoiler strip installed at the factory. The others were retro fitted. Even with the spoiler strip the quoted stall speeds are virtually the same as the F6F-5 and generally much lower than the Army types.
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What kind of turn was it? Generally I'll try to get someone to overshoot and set up a nose to nose turn so that they fly in front of me.
I'm not sure that in a nose to tail turn the 190A5 will out-turn a F4U-1D.
Interesting stuff on AHT, by the way.
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Yes, the equation I used for my calculation is:
Vs-accelerated = Vs * sqrt (g-load)
Hmmm something is askew with your chart then. If the chart you posted was IAS then you wouldn't have a difference in accelerated stall limit velocities for varying altitudes hence the curves plotted the way they are.
Tango, XO
412th FS Braunco Mustangs
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Urchin,
I did some test in the FW190A5. With the light gun package it is actually very difficult to bleed enough energy to get down below 180MPH. It makes a very fast circle at about that speed. I usually try to fly it when Buff hunting but because of the climb, dive accleration and roll I think it is a great dogfighter. I probably spend more time in Luftwable rides than you think. I usually do it for a specific mission though.
I don't have accelerated stall numbers for the FW190A5 but I do have the FW190A5 vrs F4U and F6F report. You can say the AFDU type data is Navy bias but there was one piece of data to consider. The A/C had a flight limits restriction card in it when captured.
The restrictions are as follows
466MPH below 10K
426MPH 10k to 16,400ft
360MPH 16,400ft to 25K
Also the common 1G stall speed is generally accepted at 110MPH.
Based on that you can calculate the 3G stall at 190MPH.
This is actually modeled pretty closely in AH. The problem I have have is that I believe that the F4U is modeled almost exactly the same in regards to accelerated stalls at gross weight.
As Dtango showed in his test you can do better in an F4U as long as you don't bring any fuel.
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Dtango,
Sure it does? It has 10, 15, 20, 25, 30K??? Is that what you mean?
BTW, It says Indicated Airspeed in Knots right in the middle of the chart.
(http://mywebpages.comcast.net/markw4/F4UG.jpg)
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F4UDOA, I actually think the 190A5 might be a little overmodelled. At least as far as the stall speeds go. I remember reading that the 190A4 had a listed stall speed in 'clean' configuration of 110 mph I think (might have been 120), and a 'dirty' stall of 99 mph. I can get it down to 100 mph no problem without stalling it. The only difference as far as I know between the 190a4 and the 190a5 was some radio equipment, I think. So I can't imagine why the 190a5 would have such a drastic difference in 1g clean stall speed.
I haven't really done any 'tests' other than flying as slow as I can go.
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Here's another check. Let's compare Clmax figures. Let's go with Clmax figure of 1.48 for the F4U-1D.
CLmax based on AH Model:
3g stall speed: 170 mph
Weight: 11,000 lbs
Resulting Clmax: 1.45
CLmax based on Chart:
3g stall speed: 164 mph (corrected)
Weight: 12,000 lbs
Resulting Clmax: 1.69
Looks like the AH model is closer to the 1.48 figure you've quoted as well.
Tango, XO
412th FS Braunco Mustangs
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If the airspeeds are IAS then V-n diagrams for the different alts would overlap each other on accelerated stall limits. 3g stall speed is the same IAS at alt x as it is at alt y.
Tango, XO
412th FS Braunco Mustangs
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Dtango,
Honestly, Have you ever seen any accelerations chart that looks any different? I'm not sure what you are saying but if you could show me one chart that looks like what you describe maybe that would help.
I have the F8F, F7F, P-51 and P-38 charts. They are all in the same format and all say IAS.
Do you think the chart from the pilots manual is a better representation of the F4U or AH?
The difference in Clmax is probably due to prop wash since the 1.49 number come from the NACA report with a windmilling prop at 60MPH and acceleration test are done at power with at 164MPH.
BTW, Even with that I would be glad to have the F4U acclerated stall match the NACA 1.49 as long as every other A/C in AH did also.
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Urchin,
You may be right about the 190A5. I try not to lobby HTC to "pork" AC. I would rather work on getting the undermodeled ones fixed. I happen to have a ton of data on Navy birds so it makes it easier to concentrate on the F4U, F6F etc.
I would like to see a little more feedback from HTC. I am hoping for some real changes in AH2.
Funny thing when you point out flaws in here people attack you like your insulting there religion.
These types of conversations about warbirds are much easier to have on WW2 boards because you are not insulting the ego's of engineers.
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yeah dtango i was wondering the same thing.. i would expect VERY MINOR differences due to differing reynolds number but not that severe.
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Heya Zigrat,
I still have no idea what your talking about.
I took the F6F-5 stall chart and superimposed the F4U stall chart onto it with the circles at the corresponding weights.
Try to take a F4U or F6F up and match the stall speeds at those weights power off clean or power on flaps and gear. You can't.
(http://mywebpages.comcast.net/markw4/F4UF6Fstall.jpg)
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The P-51D V-n diagram you posted is a perfect example. There's only 1 V-n curve using IAS. 3g stall speed at alt X = 3g stall speed at alt Y when you're talking IAS.
The F4U-1D charts you posted have different V-n diagrams for different alts. If it was IAS it would just be 1 curve not many so something is strange about it.
Regarding the CLmax issues..remember your own quote:
Also I asked the same question about prop slip stream to Zigrat. According to him (In my understanding anyway) it doesn't make nearly as much differance in accelerated conditions as it does in 1G flight because the AOA reduces the slipstream effect.
The CLmax figures are based on 163mph 3g stall which would negate or reduce the impact of prop induced velocity.
Finally if you we used the Clmax of 1.48 then at 11,000 lbs:
1g stall speed = 96 mph
3g stall speed = 166 mph
Clmax of 1.49 then at 11,000 lbs:
1g stall speed = 95.5 mph
3g stall speed = 165.5 mph
That's hardly a dramatic difference between the 3g 170mph , 1g 97mph figures.
Keep in mind CG also plays a part in changing CLmax so the difference could be attributed just to that alone.
Tango, XO
412th FS Braunco Mustangs
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I'm not fully understanding the F4U diagram.
On the 10,000ft and below the left boundary is from accelerated stall, top is structural limit, and right is dive speed limit. All that makes sense to me, but what I don't get is what causes the curved upper right hand boundary.
I've read that in some planes pulling G's at at speeds close to critical mach caused buffeting. But would that be happening below 10,000ft?
The P-51 diagram looks like what we see in AH, where you can pull enough G's to blackout at speeds right up to critical mach.
Another thing about that P-51 diagram. I understand that it should be applicable for all alts wrt stall limit, but I doubt the dive limit was 505IAS at all alts. IIRC the P-47 dive limit was 500IAS below 10,000ft, subtracting 50mph for every 5,000ft above that.
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Originally posted by Regurge
Another thing about that P-51 diagram. I understand that it should be applicable for all alts wrt stall limit, but I doubt the dive limit was 505IAS at all alts.
You're right about the dive limits. The chart I have shows the following:
505 @ 5,000 ft.
480 @ 10,000 ft.
400 @ 20,000 ft.
330 @ 30,000 ft. (I think - the second digit is a little fuzzy.)
260 @ 40,000 ft.
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Yep, you guys are correct regarding the max speed limits. My statement of "having 1 V-n curve" is not accurate. Stall limits would be the same at IAS for various alts with different max speed limit bound on the right side of the curves.
Tango, XO
412th FS Braunco Mustangs
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Dtango,
The CLmax figures are based on 163mph 3g stall which would negate or reduce the impact of prop induced velocity.
Finally if you we used the Clmax of 1.48 then at 11,000 lbs:
1g stall speed = 96 mph
3g stall speed = 166 mph
Clmax of 1.49 then at 11,000 lbs:
1g stall speed = 95.5 mph
3g stall speed = 165.5 mph
That's hardly a dramatic difference between the 3g 170mph , 1g 97mph figures.
I agree, it's not a huge difference if you compare the 11,000LBS AH results with the 12,000LBS chart. The difference is the weight is lower by 1,000LBS to achieve the same acceration results. If you recalculate what the chart determines for 11,000lbs the differance is much greater. You would achieve a 3G stall at 150MPH so the differance is actually 20MPH not 5MPH.
And to quote myself
Also I asked the same question about prop slip stream to Zigrat. According to him (In my understanding anyway) it doesn't make nearly as much differance in accelerated conditions as it does in 1G flight because the AOA reduces the slipstream effect.
I do believe that. But as I said, not nearly as much of an effect. I didn't say that it had no effect at all. Just look at how NACA did their Clmax test. At 60MPH prop installed and windmilling. Well in and accelerated stall there will be increased airflow over the wing. At what speed I have no idea. I'm guessing more than 60MPH less than 164MPH. But that difference can account for an reasonable increase in Clmax enough to bring the 3G stall from a calculated 173MPH down to 164MPH at 12,000LBS.
Again this is my opinion based on not only the chart I provided and my very limited understanding of how things work but on two other pieces of source documented flight test that show the F4U-1/1D/4 accelerated stall to be at least as low as what is represented on the chart.
One is a British document on 4G acclerated stalls and the other is from a modern evaluation of the F6F-5, FG-1D, P-51D and P-47D.
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The shape of the flight envelope is caused by two things. Critical mach number decreases when g load increases and relative Clmax decreases (in most cases) when mach number increases. 1 g stall speed in IAS stays quite constant but at higher speeds also accelerated stall limits decrease for given IAS speeds. See NACA reports mentioned above.
I also compared AH 1.06 to 1.14: No noticeable difference in the stall speeds of the F4U-1D. At 10k and 200mph IAS it stalls 3,7 g on pull up test, testing is just a bit more difficult because accelometer appears to be more sensitive when internal view is used for films.
Stall speeds appear to be same in the turns and pull ups for given g load. In the real world airplanes reach higher Clmax on pull ups because plane yaws a bit in level turn. As an example see mentioned NACA reports.
gripen
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dang! Im getting dizzy here....
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wow gripen i didnt look at that stuff till now very interesting articles!
the reduction in clmax with mach number at low (<.6) mach is very surprising to me, prandtl glaurt rule says lift curve slope will increase due to compressability and i guess i just assumed that alpha(stall) didnt change much so the OPPOSITE trend was true. i'm gonna read over these papers more carefuly tomorrow.
f4u for the reason why the prop wash isnt as important at high velocities i will try to sum it up briefly
the reason you get artificially higher clmax from prop is due to the fact that local flow velocity is higher than free stream. the section lift coefficient isnt really higher, but you are getting more lift since loval vinf is higher, and when you use the reference flight velocity for calculations it sppears that clmax is higher than reality.
this effect degrades with velocity for 2 reasons:
1) propeller thrust decreases with velocity. power = thrust * velocity so for constant power as velocity increases thrust decreases
since thrust is decreasing , the change in momentum imparted to the air by the propeller decreases (the delta v is smaller) so this leads to smaller increases in local velocity in the prop wash
also the % change as a fraction of freestream gets smaller as freestream increases, so you can see that these 2 effects combined mean that prop wash effects will rapidly decay with speed. they will, however, be quite strong in low speed configurations (ie lets say a missed approach by a f4u)
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Yeah, I've been looking over those reports pointed out by Gripen. I was puzzled by them before. After reading 1044 a couple of times however I think I understand.
That report was a start of the analysis to indicate why Re effect on increasing Clmax is bound. So in other words it begans to try to explain why the following is true.
"We note that as Reynolds number increases, the maximum lift coefficient increases. But this does not occur indefinitely; when flows become very turbulent, the maximum lift coefficient begins to drop and so does the overall lift coefficient."
In other words prandlt-glauert compressibility correction stops at a certain point. [edit: actually thinking about it now I'm not sure if this is an accurate statement!]
1044 goes about this by treating mach number or reynolds number as independent variables. The gotcha is it varies one while holding the other constant.
Check out NACA Report 1299 done the following year:
Naca 1299 (http://naca.larc.nasa.gov/reports/1947/naca-tn-1299/)
1299 has charts with Clmax plotted with Re and mach as dependent variables. Makes more sense to a simpleton like me!
1299 has real nice page on concluding remarks that spells things out nicely.
Tango, XO
412th FS Braunco Mustangs
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IMHO a good article on compressebility corrected envelopes can be found from the "Aero Digest" magazine, September 1, 1945 ("Computation of Compressibility Effect on the Flight Envelope" by H. R. Foottit). Example calculations in the article are for the P-47. I believe most air museums and technical universities have Aero Digest volumes in their collections.
gripen
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Thanks gripen. I'll check that article out.
Tango, XO
412th FS Braunco Mustangs
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Zigrat,
Why are accerated stall numbers consistantly higher the clmax would seemingly allow?
IE the F4U 12,000lns 3G stall at 164MPH. I can provide other simialr examples as well.
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http://www.hitechcreations.com/forums/showthread.php?s=&threadid=87239
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Hi Dtango,
>If the airspeeds are IAS then V-n diagrams for the different alts would overlap each other on accelerated stall limits. 3g stall speed is the same IAS at alt x as it is at alt y.
Did we already correct for compressibility error in the IAS reading? If not, maybe this is the factor spreading out the stall speeds at different altitudes.
Regards,
Henning (HoHun)
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Yeah, that's a good question. I don't know if they corrected for it or not. I'm guessing not since the chart says "IAS". Just referring to my EAS correction chart though at 200 kts CAS between 10K is roughly -1 kt and at 20K it is roughly -3 kts so it doesn't make up the 10 kt difference between 10K-20K. However I haven't tried applying the mach number correction mentioned by gripen on Clmax to see what the results would be on the curves.
Tango, XO
412th FS Braunco Mustangs